The invention relates generally to an electromagnetic or permanent-magnetic rail brake, and more particularly to a linear eddy current brake for rail vehicles.
In modern wheel/rail engineering, there is demand for brake technologies which have a brake force that is as much as possible independent of the coefficient of adhesion between the wheel and the rail. Linear eddy current brakes naturally meet this requirement in an ideal fashion because, as non-contact service brakes, they are absolutely independent of the coefficient of adhesion.
A short introduction into the technology of the eddy current brakes for rail vehicles--whose function is based on the law of induction--is found, for example, in the book by Saumweber, et al. "AET--Archiv fur Eisenbahntechnik (Archive for Railway Technology)"--Hestra Publishers, Volume 43, Chapter 2.5.2. Eddy current brakes consist of an iron yoke with several pole cores. Electric coils magnetically excite the brake such that magnetic north and south poles are generated in an alternating manner. When the excited eddy current brake is moved along the rail--that is, during a braking--, electromagnetic fields and eddy currents are generated as a result of the changes of the time rate of flow. The secondary magnetic field caused by the eddy currents is opposed to the magnetic field of the brake. The resulting horizontal force component which acts opposite to the travelling direction is the brake force.
Despite the important advantage of this brake of having no contact with respect to rail, the practical use of eddy current brakes in large part is delayed by the fact that the compatibility of the brake with the existing operating equipment of various railroad operators can still be optimized.
A problem of the above-mentioned type, which results in serious difficulties during the practical application, is the interfering influence of the eddy current brakes on electromagnetic axle counters and/or similar sensing devices.
This problem is described in detail in European Patent Document EP 0 309 651. A large portion of the currently existing track sections of the varied railroad operators have rails which are provided with axle counting sensors laterally below the rail surface. Generally, electromagnetic sensors are used for the axle counting. That is, a transmitter sends out an electromagnetic alternating field (of a frequency of 5 to typically 43 kHz) and, when a metal wheel travels over a sensor arranged on the opposite side of the rail, the sensor registers changes of the electric field, which are caused by the metal wheel, with respect to the amplitude and the direction as counting pulses. A train passing through the sensor arrangements triggers a counting pulse in the sensors by each axle or wheel passing there through. If, during a pass through locally mutually separate axle counters, different counting results are registered, the track section is blocked for the following train.
Since, during a braking, eddy current brakes are lowered from a high position into a low position just above the rail, they may also trigger counting pulses in the axle counting sensors during the braking. However, they trigger counting pulses only in their low position (thus, during the braking) but not in their high position. Eddy current brakes may therefore falsify the result of an axle count and stop a train for no reason.
For solving this problem, European Patent Document EP 0 309 651 A2 suggests that guiding plates made of a ferromagnetic material be mounted on the outside in the area of the lower longitudinal edges of each coil of the brake magnet. These guiding plates each extend along the lower corner edges of the exciter coil. Although the suggested solution eases the problem, faulty signals cannot be excluded to an extent required for a controlled train operation.
From Austrian Patent Document 317 290, corresponding to U.S. Pat. No. 3,805,927, an electromagnetic rail brake is known in which a rod made of a ferromagnetic material extends along the length of the electromagnetic rail brake to reduce disturbing influences. This solution also does not meet the requirements of a high-speed traffic of eliminating disturbances from the rail operation.
The invention is based on the problem of providing an electromagnetic or permanent-magnetic rail brake--particularly an eddy current brake--for rail vehicles which does not interfere with sensing devices, such as axle counters, during braking operations.
The invention implements particularly an eddy current brake for rail vehicles having at least one exciter coil which has a coil around a pole core and also has a device for holding the coil and/or for the protection against outside environmental influences. The pole core and/or the protection device is composed of individual components which are at least largely electrically insulated with respect to one another.
The division into separate individual components interrupts the transmission of a transmitted signal from a transmitter on one side of the rail to a receiver on the other side of the rail. Thus, virtually no more interfering signals occur and the use of the eddy current brake becomes possible in a large portion of the existing track systems. This basically constructively simple measure effectively prevents interfering signals. The invention therefore provides a decisive step in the penetration of the market by means of the technically advantageous eddy current brake technology.
A large number of the axle counters, which are currently used in practices are designed such that a metal wheel passing though the sensor in the receiver section produces a clearly recordable voltage change; for example, in one embodiment of the sensor, a voltage increase. This effect is prevented by the invention. In this variant, a weakening of the signal may even take place by the brake according to the invention. Counting pulses are no longer triggered.
According to another embodiment of the invention, the protection device is designed as a multipart metal housing, in which case the individual metal sections are insulated with respect to one another in the mounted position of the brake in which the longitudinal axis of the brake is aligned essentially along the longitudinal axis of the rail. Correspondingly, it is advantageous for the pole core to have at least two metal plates which are essentially insulated with respect to one another in the mounted position of the brake. Because of the skin effect, the wave transmission takes place essentially on the surface of the metal components. The division into individual layers effectively interrupts this transmission.
According to another embodiment of the invention, at least one of the metal plates is ferromagnetic. Steel can be selected for reaching good electric transmission characteristics. In this case, the metal plates are arranged in a plane perpendicular to the longitudinal axis of the rail.
In another embodiment, steel plates of the pole core are separated from one another by transformer plates. For example, five steel plates and four transformer plates are used. This embodiment achieves very good results with respect to the freedom from disturbances of axle counters without high demands constructively on the manufacturing of the pole core that, for reasons of cost, an implementation of the product would be made more difficult.
A metal housing is generally used for protecting the coils. According to the invention, it was found to be particularly advantageous for the metal housing to have lateral surfaces which are open transversely to the longitudinal axis of the brake. The partially open lateral surfaces also have an advantageous effect on the field distribution (short-circuit effect) and promote the effect of the laminated core. In further embodiments of the invention, at least one exciter coil is arranged in a housing made of glass fiber reinforced plastic and is fastened by a U-shaped carrying device on a brake anchor plate; and/or the metal plates are screwed to one another and/or are glued to one another, and are therefore mechanically connected with one another in a non-conductive manner.
By the invention, an eddy current brake (or a rail vehicle with such a brake) can be implemented in an advantageous manner which meets the requirements with respect to the freedom from disturbances of most different high-speed railway lines, such as the ICE-train and the TGV-train.
In the following, the invention will be described in detail with reference to the drawing by means of embodiments, in which case additional advantages and possibilities of the invention also become clear.